History

Supercritical fluids have been known (Table 1) since Baron Cagniard de la Tour observed in 1822 that, above a certain temperature, a liquid can be converted to a gas without the appearance of a meniscus. In 1869, Andrews fully characterized the critical point in terms of critical temperature Tc and critical

Critical point Supercritical

Table 1 Advances in supercritical fluid chromatography

Cagniard de la Tour

Discovery of supercritical 1822

state

Andrews

Characterization of

1869

critical point

Hannay and Hogarth

Increased solubility

1879

in supercritical fluids

reported

Lovelock

SFC suggested

1958

Klesper

Demonstration of SFC

1962

Giddings, Sie

Development of dense

1966-69

and Rijnders

gas GC and SFC

Sie, van Beersum

FID used in SFC

1966

and Rijnders

Sie and Rijnders

First use of term 'SFC'

1967

UV/visible detector used

1967

in SFC

Jentoft and Gouw

Pressure programming

1978

demonstrated

Randall and Wahrhaftig

SFC coupled to mass

1978

spectrometry

Novotny and Lee

Capillary column SFC

1981

demonstrated

Commercial packed

1982

column SFC

Commercial capillary

1986

column SFC

pressure Pc. Hannay and Hogarth observed in 1879 that metal halides are soluble in ethanol above the critical point, and as early as 1897 Vuillard reviewed solubility in supercritical fluids. Isolated examples of the use of near-critical solvents for separation appeared between 1930 and 1960; more extensive applications, especially to natural products with the pharmacologically acceptable carbon dioxide have since appeared, based on extensive studies of solubility in supercritical solvents and on the properties of solutions. In parallel with SFC, analytical supercritical fluid extraction (SFE) has been extensively developed as a sample preparation technique.

The original idea for SFC was suggested by Lovelock at an international meeting in 1958, before Klesper, Corwin and Turner separated involatile porphyrins in 1962 using supercritical chlorofluoro-carbons at pressures up to 136 bar as mobile phase. In 1966, Sie and Rijnders developed both adsorption and partition chromatography using carbon dioxide, «-pentane and isopropanol at temperatures up to 245°C and pressures up to 80 bar.

The advantages of carbon dioxide as a mobile phase were quickly realised: it is an inexpensive material with good solvent properties, convenient Tc and Pc, non-combustible, easily delivered by pumping the liquid, and available in high purity. Although other compounds have since been employed as mobile phases (e.g. N2O, SF6, NH3, «-butane and «-pentane, xenon, and various fluorocarbons and chlorofluoro-carbons), CO2 has remained the most popular and widely used. Because of the variation of solubility with density and hence pressure, Rijnders suggested in 1967 that pressure programming in SFC should have a similar effect to temperature programming in GC.

In 1970, Jentoft and Gouw constructed a versatile high-resolution SFC chromatograph with a pressure-programming facility for packed columns up to 4-m long and «-pentane-methanol mobile phase for temperatures up to 215°C and pressures up to 650 bar; detection was by UV absorption. Styrene oligomers up to « = 32 could be analysed with this system. The affinities between GC with a dense gas as mobile phase and SFC were discussed and developed by Gid-dings between 1966 and 1969.

Novotny pointed out in 1971 the serious limitations in SFC of the pressure gradient generated by the column packing, and realized that SFC should be possible on capillary columns with a much smaller pressure drop. In 1981, Novotny and Lee demonstrated capillary column SFC equipment. Commercial equipment for packed column SFC became available in 1982, and for capillary SFC in 1986.

The 1980-90 period was one of rapid growth in the theory, instrumentation and applications of SFC. A multi-authored text edited by Lee and Markides appeared in 1990 summarizing the state of the art, and remains authoritative. Two series of international conferences on SFC and SFE, one based in USA and the other in Europe began in 1988 and continue.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

Get My Free Ebook


Post a comment